Crystal oscillator circuits are widely used in industry, and perform the function of producing a steady and stable, periodic time-varying waveform which is used as the timing signal for a given electronic circuit or a clock signal for a system timing.
A conventional crystal oscillator solution uses a fixed amount of current during startup and during normal operation. The amount of current necessary for startup is greater than that needed for normal operation; however, the conventional solution continues to use the greater amount of current. A crystal oscillator circuit requires a large amount of current to bring the crystal oscillator to a steady state operation where periodic waveforms with full swing are generated from a startup condition where the external and internal circuitry initial startup is from a non steady state operation. Once the steady state oscillation operation is reached, the crystal oscillator circuitry only needs to provides small amounts of current in order to compensate the losses due to the quartz crystal itself so to sustain the oscillation. The first purpose of crystal oscillator amplifier circuits is to bring about a steady and periodic oscillation from a startup condition where there exists no oscillation, and the second purpose is to sustain periodic oscillation once the steady oscillation is reached. The amount of current necessary to guarantee the first condition above is generally several multiples greater than the current necessary to guarantee the second condition. In general, conventional crystal oscillator topologies are designed to consume current to guarantee the first condition even after a steady state oscillation is reached. This creates unnecessarily large amounts of current consumption during steady state condition since this current consumption for startup is much larger than necessary for steady state operation.
It would be desirable to have a crystal oscillator circuit where the current consumption of the gain element is adjustable. In order to achieve a better overall current consumption, the crystal oscillator will be allowed to consume a large amount of current to get to steady state oscillation condition from startup. Once the steady state oscillation is achieved, the circuitry can be programmed to provide only the amount of current necessary to sustain the oscillation.